This invention relates to a heat exchanger.
A heat exchanger is commonly used for refrigeration, cooling, and heating applications. For these applications, the heat exchanger transfers heat from one fluid to another fluid without the fluids intermingling. The fluid may be a gas or a liquid. For certain high-pressure applications involving CO2 gas, manufacturers have used a tube-in-tube design for a heat exchanger. Essentially, the heat exchanger is one tube containing one fluid surrounded by another larger tube containing the other fluid. For example, CO2 gas may circulate within the inner tube while water may circulate in the surrounding tube. Heat is exchanged through the surface of the inner tube.
For a high-pressure application, tube diameters have to be kept small (less than ⅜ of an inch) to maintain a reasonable wall thickness. For large capacity systems, these tubes are problematic because the heat exchanger requires a large number of parallel circuits. As a consequence, the length of the heat exchanger may be very long.
In addition, water used in the heat exchanger may be used subsequently for consumption or for a sanitary process. It is critical that the water not be contaminated during the heat exchange process. The conventional tube within a tube design poses a risk of water contamination because the tube for one fluid, say water, surrounds the tube of the other heat exchange fluid. Accordingly, rupture of the inner tube within the larger tube would cause contamination of the water in the larger tube.
One proposed solution pipes one heat exchange fluid in a tube that twists around a straight tube having the other fluid. However, due to the different geometries of the tubes, the two tubes may have limited areas of physical contact with each other. Consequently, heat exchange is not very efficient.
The manufacture of this unique heat exchanger presents a challenge as well. Specifically, in the past, manufacturers have produced a helical tube by coiling a single tube around a fixture. In some instances, manufacturers have also coiled a single tube over itself to create multiple layers of coiled tubing in an effort to increase the surface area per linear length of heat exchanger. However, the foregoing techniques fail to coil more than one heat exchanging tube in a tight helical spiral as would be best suited for optimum heat transfer.
A need therefore exists for a heat exchanger and method of manufacturing the heat exchanger that avoids the foregoing deficiencies and improves upon the efficiency of heat exchange.